A fundamental understanding of how biological cells interact with materials would be useful for tissue engineering, and treating cardiovascular disease. A particularly exciting area of biomaterials science is the design of materials that can induce cell adhesion, spreading, and cell-cell communication. Here, we develop a new way of switching "on" and "off1 the adhesiveness of the substrate, by assembling peptide ligands on a hydrogel surface using coiled-coil peptide assemblies induced by small molecule activators, such as cations. Adhesive peptides and growth factors peptides will be linked to a hyrdogel surface on cue, using a change in activator concentration. The behavior of cells in response to surface activation will be assessed using traction force microscopy (TFM), in which the forces exerted by cells on surfaces are imaged. We will combine our adhesive technology and TFM to measure the adhesion, spreading, and cell-cell interactions of endothelial cells, a critical cell in the cardiovascular system involved in blood vessel hemostasis and angiogenesis. In aim 1, we will develop methods to assemble peptides at surfaces using coiled-coil peptide domains. Peptides we will assemble are RGD, the peptide in the cell binding domain of fibronectin;PHSRN, the fibronectin synergy site;epidermal growth factor (EGF);and vascular endothelial growth factor (VEGF). EOF and VEGF are obvious choices which have implicated in cell adhesion strengthening and angiogenesis, respectively. In aim 2, we will study how the coordinated delivery of adhesive and growth factor peptides can induce the spreading and force generation of single endothelial cells. We will measure cell spreading and force generation as a function of peptide type, peptide concentration, time, and substrate compliance, for two types of endothelial cells : bovine aortic endothelial cells and microvascular endothelial cells. We will focus on pairs of ligands, using RGD as the common peptide, and combining it with either the synergy site or a growth factor peptide. In aim 3, we will measure how the combination of adhesive and growth factor ligands can induce cell-cell communication between endothelial cells, by measuring the adhesion probability or the dispersion of cells as a function of ligand type, ligand density, time, and substrate compliance for both endothelial cell types. Finally, we will use our peptide surfaces to test the "differential adhesion hypothesis", in which cell-cell communication can be engineered through alteration in cell substrate adhesion.